JP2009167944A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection control device for an internal combustion engine, preferably suppressing the increase of NOx discharging amount when the oxygen occlusion performance of an exhaust purifying catalyst is deteriorated. <P>SOLUTION: An electronic control unit 17 prohibits renewal of a sub F/B leaning value in a high-load area where the exhaust amount becomes large when the oxygen occlusion performance of the exhaust purifying catalyst is deteriorated, and then changes a target air/fuel ratio (target output of an oxygen sensor 24) of a sub feedback control in the high-load area to a rich side rather than time when not deteriorated. Without deteriorating the leaning accuracy of the sub F/B leaning value, therefore, while keeping to tne minimum a required engine operation area changing the target air/fuel ratio, the increase of the NOx discharging amount caused by the oxygen occlusion performance of the exhaust purifying catalyst is preferably suppressed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention performs air-fuel ratio feedback control of the fuel injection amount so that the air-fuel ratio of the air-fuel mixture combusted in the internal combustion engine becomes the target air-fuel ratio based on the detection result of the exhaust oxygen concentration, and the air-fuel ratio feedback control in the air-fuel ratio feedback control The present invention relates to a fuel injection amount control device for an internal combustion engine that updates a feedback learning value based on a feedback correction amount of a fuel injection amount.

  As is well known, a three-way catalytic converter carrying a three-way catalyst using a noble metal such as platinum, palladium, or rhodium as an active substance is used as an exhaust emission control device for an on-board internal combustion engine. The three-way catalyst simultaneously performs oxidation of carbon monoxide (CO) and hydrocarbon (HC) in the exhaust gas and reduction of nitrogen oxide (NOx), which are harmless carbon dioxide (CO2) and water (H2O). ) And nitrogen (N2) to purify the exhaust gas. Exhaust gas purification using such a three-way catalyst is most effectively performed when the oxygen concentration in the catalyst atmosphere becomes a value when the air-fuel ratio of the air-fuel mixture burned in the internal combustion engine is the stoichiometric air-fuel ratio. Therefore, in an internal combustion engine that employs a three-way catalyst as an exhaust purification device, air-fuel ratio feedback control is performed to maintain the air-fuel ratio of the air-fuel mixture to be burned within a certain narrow width (window) near the stoichiometric air-fuel ratio. Yes. In such air-fuel ratio feedback control, the fuel injection amount is feedback-corrected based on the output of the oxygen sensor that detects the exhaust oxygen concentration, thereby maintaining the air-fuel ratio in the above-mentioned window and good reaction conditions for exhaust purification. Is producing.

  By the way, microscopically, harmful components in the exhaust gas are purified by adsorbing on the catalytic noble metal or promoter oxide on the carrier and causing a catalytic reaction thereon. Therefore, in order to ensure high exhaust purification performance, the reaction conditions in the micro space where the catalytic reaction occurs, especially the conditions of the gas composition, are good while maintaining the exhaust oxygen concentration at the macro level by air-fuel ratio feedback control. It is necessary to secure it. Therefore, in recent years, the catalyst layer itself has a function of controlling the air-fuel ratio in the micro space. The achievement of such a function is achieved by supporting a promoter such as cerium having oxygen storage capacity (OSC) on a three-way catalytic converter. In other words, these promoters store oxygen when the amount of oxygen in the surrounding area is large, and release the stored oxygen when the amount of oxygen in the surrounding area is small, thereby appropriately controlling the surrounding oxygen concentration at a micro level. It is supposed to be.

  Now, the oxygen storage capacity of such a three-way catalyst gradually decreases with long-term use. Due to the decrease in the oxygen storage capacity due to such deterioration over time, the exhaust purification performance of the catalyst decreases, and the amount of CO, HC, NOx that is exhausted to the outside air without being completely purified increases. Note that the NOx emission tends to increase particularly remarkably due to the decrease in oxygen storage capacity of the catalyst. Incidentally, conventionally, as an apparatus for determining the degree of deterioration with time of such an exhaust purification catalyst, those described in Patent Document 1 and Patent Document 2 have been proposed.

Conventionally, an apparatus described in Patent Document 3 has been proposed as an apparatus for suppressing deterioration of emission during catalyst deterioration. In the apparatus described in the document 3, the proportional constant and integral constant of the feedback correction coefficient of the fuel injection amount in the air-fuel ratio feedback control are corrected according to the degree of deterioration of the exhaust purification catalyst, and the rich period and lean period of the air-fuel ratio are corrected. By adjusting the length in accordance with the decrease in the oxygen storage capacity of the catalyst, it is possible to suppress the deterioration of emission during catalyst deterioration.
Japanese Patent Laid-Open No. 2005-207286 JP 2005-194981 A JP 2004-019467 A

  It is certainly possible to suppress the deterioration of emission when the catalyst's oxygen storage capacity declines to some extent by correcting the proportional constant and integral constant of the feedback correction coefficient according to the degree of deterioration of the catalyst as in the conventional device above. It is. However, such correction of the proportionality constant and integral constant alone has a limit to the effect of suppressing the deterioration of emissions when the catalyst is deteriorated. In particular, the remarkable increase in NOx emission when the oxygen storage capacity of the catalyst is reduced can still be sufficiently suppressed. There is no actual situation.

  The present invention has been made in view of the current situation, and a problem to be solved is an internal combustion engine that can suitably suppress an increase in NOx emission when the oxygen storage capacity of the exhaust purification catalyst is reduced. An object of the present invention is to provide a fuel injection control device.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
In order to solve the above-mentioned problem, the invention according to claim 1 is an air-fuel ratio feedback of the fuel injection amount so that the air-fuel ratio of the air-fuel mixture burned in the internal combustion engine is set to the target air-fuel ratio based on the detection result of the exhaust oxygen concentration. In the fuel injection amount control device for an internal combustion engine that performs control and updates the feedback learning value based on the feedback correction value of the fuel injection amount in the air-fuel ratio feedback control, when the oxygen storage capacity of the exhaust purification catalyst decreases, The feedback in the engine operation region in which the target air-fuel ratio in the engine operation region where the displacement is large is changed to a richer side than when the oxygen storage capacity is not lowered, and the target air-fuel ratio is changed to the rich side. The gist is to prohibit the update of the learning value.

  In the above configuration, when the oxygen storage capacity of the exhaust purification catalyst is reduced, the update of the feedback learning value based on the feedback correction value of the fuel injection amount in the air-fuel ratio feedback control is prohibited in the engine operation region where the exhaust amount becomes large. Become so. Therefore, in such an engine operation region, even if the target air-fuel ratio of the air-fuel ratio feedback control is changed, the learning accuracy of the feedback learning value is not affected.

  In the above configuration, the target air-fuel ratio of the air-fuel ratio feedback control is changed to the rich side in the engine operation region outside the learning region due to such restriction of the learning region. When the target air-fuel ratio is changed to the rich side in this way, the combustion of the internal combustion engine is performed at a richer air-fuel ratio than usual, and the NOx emission amount is reduced. Such a change in the target air-fuel ratio is an engine operating region in which the amount of exhaust gas is large and therefore the amount of NOx generated by combustion is also large, so the influence of the NOx emission amount on the overall emission performance of the internal combustion engine is significant. Therefore, the increase in the NOx emission amount due to the decrease in the oxygen storage capacity of the exhaust purification catalyst is effectively suppressed while keeping the engine operating range for changing the target air-fuel ratio to the minimum necessary. In addition, in the engine operation region in which the target air-fuel ratio is changed, updating of the feedback learning value is prohibited, so that the learning accuracy of the feedback learning value due to the change is not reduced. Therefore, according to the above configuration, it is possible to suitably suppress an increase in the NOx emission amount when the oxygen storage capacity of the exhaust purification catalyst is lowered.

  According to a second aspect of the present invention, in the fuel injection control device for an internal combustion engine according to the first aspect, in the air-fuel ratio feedback control, a main feedback based on a detection result of an exhaust oxygen concentration upstream of the exhaust purification catalyst. Control and sub-feedback control based on the detection result of the exhaust oxygen concentration on the exhaust downstream side of the exhaust purification catalyst, and the change of the target air-fuel ratio and the feedback when the oxygen storage capacity of the exhaust purification catalyst is reduced The gist is to prohibit the update of the learning value for the target air-fuel ratio and the feedback learning value for the sub-feedback control.

  In the above-described configuration, there is empty feedback through two feedbacks, main feedback based on the detection result of the exhaust oxygen concentration upstream of the exhaust purification catalyst and rust feedback based on the detection result of the exhaust oxygen concentration downstream of the exhaust purification catalyst. Fuel ratio feedback control is performed. When performing air-fuel ratio feedback control in this manner, the change of the target air-fuel ratio and the prohibition of updating the feedback learning value when the oxygen storage capacity of the exhaust purification catalyst in the fuel injection control device for an internal combustion engine according to claim 1 is reduced are: The target air-fuel ratio and the feedback learning value for the sub-feedback control can be performed as targets.

  In order to solve the above-mentioned problem, the invention according to claim 3 is directed to an air-fuel ratio of the fuel injection amount so that the air-fuel ratio of the air-fuel mixture burned in the internal combustion engine is set to the target air-fuel ratio based on the detection result of the exhaust oxygen concentration. In a fuel injection amount control device for an internal combustion engine that performs feedback control and updates a feedback learning value based on a feedback correction value of the fuel injection amount in the air-fuel ratio feedback control, when the oxygen storage capacity of the exhaust purification catalyst decreases The target air-fuel ratio in the engine operation region where the displacement is large is changed to the rich side as compared with the time when the oxygen storage capacity is not lowered, and the target air-fuel ratio is changed to the rich side. The gist is to reduce the update degree of the feedback learning value as compared to other engine operation regions.

  In the above configuration, when the oxygen storage capacity of the exhaust purification catalyst is reduced, in the engine operation region where the exhaust amount becomes large, the update degree of the feedback learning value based on the feedback correction value of the fuel injection amount in the air-fuel ratio feedback control is different. The engine operating range will be lowered. For this reason, in such an engine operation region, the update of the feedback learning value is limited, so that the influence of the change of the target air-fuel ratio of the air-fuel ratio feedback control on the learning accuracy of the feedback learning value can be suppressed low.

  In the above configuration, the target air-fuel ratio of the air-fuel ratio feedback control is changed to the rich side in the engine operation region where learning of the feedback learning value is limited. When the target air-fuel ratio is changed to the rich side in this way, the combustion of the internal combustion engine is performed at a richer air-fuel ratio than usual, and the NOx emission amount is reduced. Such a change in the target air-fuel ratio is an engine operating region in which the amount of exhaust gas is large and therefore the amount of NOx generated by combustion is also large, so the influence of the NOx emission amount on the overall emission performance of the internal combustion engine is significant. Therefore, the increase in the NOx emission amount due to the decrease in the oxygen storage capacity of the exhaust purification catalyst is effectively suppressed while keeping the engine operating range for changing the target air-fuel ratio to the minimum necessary. In addition, in the engine operation region in which the target air-fuel ratio is changed, the update of the feedback learning value is limited, and a decrease in the learning accuracy of the feedback learning value due to the change is suppressed. Therefore, according to the above configuration, it is possible to suitably suppress an increase in the NOx emission amount when the oxygen storage capacity of the exhaust purification catalyst is lowered.

  According to a fourth aspect of the present invention, in the fuel injection control device for an internal combustion engine according to the third aspect, in the air-fuel ratio feedback control, a main feedback based on a detection result of an exhaust oxygen concentration upstream of the exhaust purification catalyst. Control and sub-feedback control based on the detection result of the exhaust oxygen concentration on the exhaust downstream side of the exhaust purification catalyst, and the change of the target air-fuel ratio and the feedback when the oxygen storage capacity of the exhaust purification catalyst is reduced The gist of the present invention is to reduce the update degree of the learning value with respect to the target air-fuel ratio and the feedback learning value of the sub feedback control.

  In the above-described configuration, there is empty feedback through two feedbacks, main feedback based on the detection result of the exhaust oxygen concentration upstream of the exhaust purification catalyst and rust feedback based on the detection result of the exhaust oxygen concentration downstream of the exhaust purification catalyst. Fuel ratio feedback control is performed. When air-fuel ratio feedback control is performed in this manner, the target air-fuel ratio is changed when the oxygen storage capacity of the exhaust purification catalyst in the fuel injection control device for an internal combustion engine is reduced, and the feedback learning value is updated less frequently. The target air-fuel ratio and the feedback learning value for the sub-feedback control can be performed as targets.

  According to a fifth aspect of the present invention, in the fuel injection control device for an internal combustion engine according to the second or fourth aspect, the first oxygen sensor for detecting an exhaust oxygen concentration upstream of the exhaust purification catalyst, and the exhaust gas A second oxygen sensor for detecting an exhaust oxygen concentration on the exhaust downstream side of the purification catalyst, and performing the main feedback control between an actual air fuel ratio calculated from an output of the first oxygen sensor and a target air fuel ratio. The sub-feedback control is performed by correcting the fuel injection amount according to the deviation, and the output of the first oxygen sensor is corrected according to the deviation between the output of the second oxygen sensor and the target output of the sensor. The gist of this is to do.

  When the air-fuel ratio feedback control is performed through the two feedbacks of the main feedback control and the sub-feedback control as described above, the change of the target air-fuel ratio of one of the two feedback controls is actually performed for the other feedback control. The air / fuel ratio of the engine may not be changed as desired. In that respect, when the main feedback control and the sub feedback control are performed in the above-described manner, the actual air fuel ratio can be obtained only by changing the target air fuel ratio of the sub feedback control set by the target output of the second oxygen sensor. Will be changed. Therefore, according to the above configuration, it is possible to appropriately suppress an increase in the NOx emission amount when the oxygen storage capacity of the exhaust purification catalyst is reduced without complicating the control structure.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of a fuel injection control device for an internal combustion engine according to the present invention will be described in detail with reference to FIGS. Note that the fuel injection control device of the present embodiment is applied to an in-vehicle internal combustion engine.

  In the internal combustion engine shown in FIG. 1, the amount of air taken into the combustion chamber 12 is adjusted through opening control of the throttle valve 11 installed in the intake passage 10. An air-fuel mixture of this air and fuel injected from the injector 13 is combusted in the combustion chamber 12. Exhaust gas generated by the combustion of the air-fuel mixture in the combustion chamber 12 is discharged to the exhaust passage 14 and is exhausted by the exhaust purification catalyst of the two catalytic converters (front catalytic converter 15 and rear catalytic converter 16) installed in the exhaust passage 14. Purified. In these catalytic converters (15, 16), as an exhaust purification catalyst, there is a three-way catalyst for purifying these by simultaneously oxidizing HC and CO and reducing NOx, and a promoter such as cerium having oxygen storage capacity. A higher exhaust purification performance is exhibited by the oxygen storage capacity of the promoter.

  Note that the three-way catalyst can most effectively purify HC, CO, and NOx when the oxygen concentration in the catalyst atmosphere reaches the value at the time of combustion of the air-fuel mixture at the stoichiometric air-fuel ratio. For this reason, in this internal combustion engine, air-fuel ratio feedback control according to the detection result of the exhaust oxygen concentration is executed so that the oxygen concentration in the catalyst atmosphere is maintained at an optimum value for purifying the exhaust gas.

  Such air-fuel ratio feedback control is executed by the electronic control unit 17 that controls the engine. The electronic control unit 17 temporarily stores a central processing unit (CPU) that executes various arithmetic processes related to engine control, a read-only memory (ROM) in which engine control programs and data are stored, CPU arithmetic results, and the like. And a random access memory (RAM) stored in the memory, an input / output port (I / O) for inputting / outputting signals to / from the outside, and the like.

  The input port of the electronic control unit 17 includes an accelerator sensor 18 that detects the accelerator operation amount, a throttle sensor 19 that detects the opening degree of the throttle valve 11, an air flow meter 20 that detects the intake air amount, and an engine speed. The output of the fuel pressure sensor 22 that detects the pressure (fuel pressure) of the fuel supplied to the NE sensor 21 and the injector 13 is input.

  In addition, an air-fuel ratio sensor 23 installed on the upstream side of the catalyst (exhaust upstream side of the front catalytic converter 15) and an downstream side of the catalyst (exhaust downstream side of the rear catalytic converter 16) are installed at the input port of the electronic control unit 17. The output of the oxygen sensor 24 is also input. As shown in FIG. 2, the air-fuel ratio sensor 23 outputs a voltage signal corresponding to the exhaust oxygen concentration upstream of the catalyst. The air-fuel ratio sensor 23 employed in the present embodiment has an output VAF of just “0 V” when the exhaust gas oxygen concentration on the upstream side of the catalyst is the value X when the air-fuel mixture is combusted at the stoichiometric air-fuel ratio. It is comprised so that. The oxygen sensor 24 outputs a voltage signal corresponding to the exhaust oxygen concentration on the downstream side of the catalyst. As shown in FIG. 3, the output VO of the oxygen sensor 24 changes in a step-like manner with the boundary when the exhaust oxygen concentration downstream of the catalyst is the value X when the air-fuel mixture is burned at the stoichiometric air-fuel ratio. It is supposed to be. The oxygen sensor 24 employed in the present embodiment is configured such that its output VO becomes “0.5 V” when combustion is performed at the stoichiometric air-fuel ratio.

Hereinafter, details of the air-fuel ratio feedback control executed by the electronic control unit 17 will be described.
The electronic control unit 17 basically calculates the fuel injection amount required at that time as the command injection amount Q based on the engine rotation speed and the engine load factor, and the fuel for the calculated command injection amount Q. The injector 13 is driven so that is injected. The engine speed used for calculating the command injection amount Q at this time is obtained from the detection result of the NE sensor 21. The engine load factor indicates the ratio of the current load to the maximum load of the internal combustion engine, and is calculated based on the engine speed and the intake air amount detected by the air flow meter 20.

When the injector 13 is driven in accordance with the command injection amount Q, the command injection time TAU is calculated as the energization time of the injector 13 necessary for injecting fuel for the command fuel injection amount Q. The command injection time TAU is calculated using the following equation (1).

TAU = Q × K1 × KINJA + KINJB (1)

  In the above equation (1), “K1” is the change in the fuel injection amount due to the difference in the fuel injection rate (the fuel injection amount from the injector 13 per unit time) corresponding to the pressure (fuel pressure) of the fuel supplied to the injector 13. Is a fuel pressure correction coefficient for compensating The value of the fuel pressure correction coefficient K1 is set to “1.0” when the fuel pressure is a specified reference fuel pressure, and the value increases as the fuel pressure decreases, and the value decreases as the fuel pressure increases. It has become. In addition, “KINJA” in the above equation (1) is a sensitivity coefficient, and the value indicates the energization time of the injector 13 necessary for unit amount fuel injection when the fuel pressure is the reference fuel pressure. Further, “KINJB” in the above formula (1) is an invalid injection period of the injector 13, and its value corresponds to the time from the start of energization to the injector 13 until the actual fuel injection is started. Yes.

Next, the details of the procedure for calculating the command injection amount Q will be described. The command injection amount Q includes a basic injection amount Qbase, a main feedback correction value (hereinafter referred to as “main F / B correction value”) DF, and a main feedback learning value (hereinafter referred to as “main F / B learning value”) MG ( Based on i), it is calculated using the following equation (2).

Q = Qbase + DF + MG (i) (2)

  Here, the basic injection amount Qbase is a theoretical value of the fuel injection amount necessary for setting the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 12 to the stoichiometric air-fuel ratio (= 14.7). It is obtained as a value (GA / 14.7) obtained by dividing the intake air amount GA detected by the air flow meter 20 by the theoretical air-fuel ratio. The main F / B correction value DF is a correction value that is increased or decreased in accordance with the deviation between the actual air-fuel ratio and the stoichiometric air-fuel ratio that is grasped from the detection result of the exhaust gas oxygen concentration upstream of the catalyst by the air-fuel ratio sensor 23. The command injection amount Q and consequently the command injection time TAU are increased or decreased so that the actual air fuel ratio is maintained in the vicinity of the theoretical air fuel ratio by increasing or decreasing the main F / B correction value DF. Further, the main F / B learning value MG (i) is a steady state between the theoretical value and the actual value of the fuel injection amount required to obtain the theoretical air-fuel ratio due to individual differences in the fuel system and intake system of the internal combustion engine and deterioration over time. The deviation is compensated, and the value is updated according to the value of the main F / B correction value DF.

More specifically, the main F / B correction value DF is calculated using the following equation (3) based on the fuel amount deviation ΔQ, the proportional gain Gp, the fuel amount deviation integrated value ΣΔQ, and the integral gain Gi. The

DF = ΔQ × Gp + ΣΔQ × Gi (3)

The first term “ΔQ × Gp” on the right side of Equation (3) is a proportional term that takes a value proportional to the amount of deviation of the actual air-fuel ratio from the theoretical air-fuel ratio. The fuel amount deviation ΔQ in the proportional term is calculated using the following equation (4) based on the intake air amount GA, the actual air-fuel ratio ABF, and the basic injection amount Qbase. The proportional gain Gp is a constant whose value is adapted beforehand through experiments and simulations, and is set to a negative value here.

ΔQ = (GA / ABF) −Qbase (4)

  Note that the value of the actual air-fuel ratio ABF in the above equation (4) is calculated from the output VAF of the air-fuel ratio sensor 23 (strictly speaking, the output VAFs after correction in the sub feedback control). The value of the fuel amount deviation ΔQ thus obtained is a value obtained by subtracting the theoretical fuel amount necessary for obtaining the theoretical air-fuel ratio from the actually burned fuel amount.

  Further, the second term “ΣΔQ × Gi” on the right side of the above equation (3) is an integral for eliminating the residual deviation of the actual air-fuel ratio from the stoichiometric air-fuel ratio, which cannot be solved only by the proportional term “ΔQ × Gp”. It is a term. The fuel amount deviation integral value ΣΔQ here is obtained as a time integral value of the fuel amount deviation ΔQ. The integral gain Gi here is a constant whose value is adapted beforehand through experiments, simulations, and the like, and is set to a negative value here.

  The main F / B correction value DF thus obtained basically decreases the basic injection amount Qbase when combustion is performed at an air-fuel ratio richer than the stoichiometric air-fuel ratio and the exhaust oxygen concentration on the upstream side of the catalyst becomes low. When the combustion is performed at an air-fuel ratio leaner than the stoichiometric air-fuel ratio and the exhaust oxygen concentration on the upstream side of the catalyst becomes high, the value is increased or decreased so as to increase the basic injection amount Qbase. Therefore, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 12 is feedback-adjusted so as to approach the stoichiometric air-fuel ratio through such increase / decrease of the main F / B correction value DF.

  On the other hand, the main F / B learning value MG (i) described above is updated in accordance with the main F / B correction value DF calculated as described above. Specifically, the main F / B learning value MG (i) is updated to the main F / B correction value DF at that time when both the following update conditions (A) and (B) are satisfied. It has come to be.

(A) The correction rate of the basic injection amount Qbase by the main F / B correction value DF, that is, the ratio of the main F / B correction value DF to the basic injection amount Qbase (= | DF / Qbase |) is sufficiently large (for example, “1 %"more than).

(B) The fluctuation amount of the main F / B correction value DF is sufficiently small.
The main F / B correction value DF comes closer to “0” depending on the result of correction using the main F / B learning value MG (i). The value of the main F / B learning value MG (i) when the main F / B correction value DF approaches “0” corresponds to the stoichiometric air-fuel ratio due to individual differences in the intake system and the fuel system and changes over time. The value corresponds to the steady deviation of the actual air-fuel ratio.

  The main F / B learning value MG (i) is calculated individually for each of a plurality of learning regions i (i = 1, 2, 3,...) Divided according to the load region of the internal combustion engine. Then, according to the engine load at that time, the corresponding learning region i is selected as the main F / B learning value MG (i) to be used.

  As described above, in the fuel injection control device for an internal combustion engine according to the present embodiment, the air-fuel ratio feedback control based on the detection result of the air-fuel ratio sensor 23 that detects the exhaust oxygen concentration upstream of the catalyst, that is, the main feedback control is performed. It is done. On the other hand, in the present embodiment, in addition to this, sub-feedback control is performed in order to suppress a decrease in accuracy of the main feedback control due to variations in output characteristics of the air-fuel ratio sensor 23 due to individual differences and changes over time.

In such sub-feedback control, the output VAF of the air-fuel ratio sensor 23 used to calculate the actual air-fuel ratio ABF used for the main feedback control is corrected in the manner shown in the following equation (5). In the following equation (5), “VAFs” indicates the output of the air-fuel ratio sensor 23 after the correction by the sub feedback control, and “VAF” indicates the output before the correction.

VAFs → VAF + VH + SG (5)

  “VH” in the above equation (5) is a sub feedback (sub F / B) correction value, and the value is increased or decreased according to the detection result of the oxygen sensor 24 installed downstream of the catalyst. Yes. Further, “SG” in the above equation (5) is a sub F / B learning value, and the value is updated according to the increase / decrease of the sub F / B correction value VH.

The sub F / B correction value VH is calculated using the following equation (6) based on the voltage deviation ΔV, the proportional gain Kp, the voltage deviation integral value ΣΔV, the integral gain Ki, the voltage differential value dV, and the differential gain Kd.

VH = ΔV × Kp + ΣΔV × Ki + dV × Kd (6)

  The first term “ΔV × Kp” on the right side of equation (6) is proportional to the deviation between the actual value of the exhaust oxygen concentration on the downstream side of the catalyst and the value when combustion is performed at the stoichiometric air-fuel ratio. It is a proportional term that takes a value. The voltage deviation ΔV in the proportional term “ΔV × Kp” is calculated as a value (= VO−tVO) obtained by subtracting the target output tVO from the actual output VO of the oxygen sensor 24. Here, the target output tVO is set to the theoretical value of the output of the oxygen sensor 24 when combustion is performed at the stoichiometric air-fuel ratio. As shown in FIG. 3, when combustion is performed at an air-fuel ratio leaner than the stoichiometric air-fuel ratio and the exhaust oxygen concentration on the downstream side of the catalyst becomes higher than the value X at the stoichiometric air-fuel ratio, the oxygen sensor 24 The output VO is smaller than the target output tVO. When combustion is performed at an air-fuel ratio richer than the stoichiometric air-fuel ratio and the exhaust gas oxygen concentration on the downstream side of the catalyst becomes lower than the value X at the stoichiometric air-fuel ratio, the output VO takes a value larger than the target output tVO. It has become. Further, the proportional gain Kp in the proportional term “ΔV × Kp” is a constant whose value is adapted in advance through experiments and simulations, and is set to a negative value here.

  Further, the second term “ΣΔV × Ki” on the right side of the above equation (6) is an integral for eliminating the residual deviation of the actual air-fuel ratio with respect to the theoretical air-fuel ratio, which cannot be solved only by the proportional term “ΔV × Kp”. It is a term. The voltage deviation integral value ΣΔV here is obtained as a time integral value of the voltage deviation ΔV. Further, the integral gain Ki here is a constant whose value is adapted in advance through experiments and simulations, and is set to a negative value here.

  Further, the third term “dV × Kd” on the right side of the above equation (6) is a differential term for enhancing the response when the exhaust oxygen concentration on the downstream side of the catalyst is converged to the value at the stoichiometric air-fuel ratio. The voltage differential value dV here is obtained as a time differential value of the output VO of the oxygen sensor 24, and the value represents the amount of change per unit time of the output VO. The differential gain Kd in the differential term “dV × Kd” is a constant whose value is adapted beforehand through experiments, simulations, and the like, and is set to a negative value here.

  The sub F / B correction value VH obtained in this way is the value of the output VO of the oxygen sensor 24 when the combustion is performed at an air-fuel ratio richer than the stoichiometric air-fuel ratio and the exhaust oxygen concentration on the downstream side of the catalyst becomes low. Since it becomes larger than the output tVO, its value is decreased so as to decrease and correct the output VAF of the air-fuel ratio sensor 23 used for calculation of the actual air-fuel ratio ABF. Therefore, the calculated value of the actual air-fuel ratio ABF at this time is corrected to a value indicating a richer air-fuel ratio, and the main F / B correction value DF is so corrected that the basic injection amount Qbase is further reduced. The value of will be decreased. On the other hand, when combustion is performed at an air-fuel ratio leaner than the stoichiometric air-fuel ratio and the exhaust gas oxygen concentration on the downstream side of the catalyst becomes high, the output VO of the oxygen sensor 24 becomes smaller than the target output tVO, so that the actual air-fuel ratio ABF The value is increased so as to increase and correct the output VAF of the air-fuel ratio sensor 23 used for the calculation of the above. Therefore, the calculated value of the actual air-fuel ratio ABF at this time is corrected to a value indicating a leaner air-fuel ratio, and the main F / B correction value DF so that the basic injection amount Qbase is further corrected to increase. The value of is increased. Therefore, depending on the increase / decrease in the sub F / B correction value VH, the fuel injection amount is feedback adjusted so that the exhaust oxygen concentration on the downstream side of the catalyst becomes the value when combustion is performed at the stoichiometric air-fuel ratio. Become.

  On the other hand, the update of the sub F / B learning value SG according to the increase / decrease of the sub F / B correction value VH is performed in the following manner. That is, when updating the sub F / B learning value SG, first, a gradual change value of the sub F / B correction value VH is calculated, and further, an upper limit guard and a lower limit guard are applied to the gradual change value to calculate the update amount SGK. The Then, the update amount SGK is set as the latest value obtained by adding the update amount SGK to the sub F / B learning value SG before update, so that the sub F / B learning value SG is updated ("updated SG"). ← “SG before update” + SGK).

  Depending on the sub F / B learning value SG updated in this way, the value of the sub F / B correction value VH becomes closer to “0”. Then, the value of the sub F / B learning value SG when the value of the sub F / B correction value VH approaches “0” depends on individual differences in the output characteristics of the air-fuel ratio sensor 23 and the exhaust gas purification characteristics of the catalyst, and changes over time. The resulting value corresponds to the steady-state deviation of the actual air-fuel ratio with respect to the stoichiometric air-fuel ratio.

  FIG. 4 shows the oxygen storage capacity of the exhaust purification catalyst and the NMHC (non-methane hydrocarbon) emission amount according to the travel distance of the vehicle when the air-fuel ratio feedback control in the above-described mode is performed without change. And the transition of NOx emissions. The figure also shows the regulation values for the NMHC emission amount and the NOx emission amount. As such regulation values, there are a 50 km mile regulation value that is applied when the vehicle mileage is less than 50 km miles, and a 120 km mile regulation value that is applied when the vehicle mileage is 50 km miles or more and less than 120 km miles, When the mileage exceeds 50 kilomiles, these emissions regulations are relaxed one step.

  As shown in the figure, the oxygen storage capacity of the exhaust purification catalyst gradually decreases as the travel distance of the vehicle increases. The electronic control unit 17 monitors the degree of decrease in the oxygen storage capacity of the exhaust purification catalyst by its self-diagnosis function. When the oxygen storage capacity decreases below a specified warning value, the electronic control unit 17 turns on the warning lamp and turns on the catalytic converter. The driver is notified that the replacement of (15, 16) is necessary.

  As the exhaust gas purifying catalyst has a reduced oxygen storage capacity, its exhaust gas purifying performance decreases. As shown in the figure, the NMHC emission amount and the NOx emission amount increase as the vehicle travel distance increases. It becomes like this. In accordance with the decrease in the oxygen storage capacity of the exhaust purification catalyst at this time, the increase in the NOx emission amount tends to increase more significantly than the NMHC emission amount. Therefore, while it is possible to secure a relatively large margin for regulation with respect to the NMHC emission amount, it is difficult to ensure a sufficient margin for regulation with respect to the NOx emission amount.

  By the way, with the above three-way catalyst, the oxidation reaction of CO and HC is further promoted and the purification rate is improved in the catalyst atmosphere when the combustion is performed at an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio. However, the NOx purification rate decreases. Further, in a catalyst atmosphere when combustion is performed at an air / fuel ratio that is somewhat richer than the stoichiometric air / fuel ratio, the NOx reduction reaction is further promoted and its purification rate is improved, but the CO and HC purification rates are reduced. . That is, in the catalyst atmosphere when combustion is performed at the stoichiometric air-fuel ratio, the overall exhaust purification effect when the CO, HC, NOx purification rates are viewed in total can be obtained to the maximum. Therefore, when focusing only on the suppression of the increase in the NOx emission amount, this can be achieved by making the air-fuel ratio of the air-fuel mixture to be burned slightly richer than the stoichiometric air-fuel ratio.

  On the other hand, if the NOx emission amount in the engine high load region where the exhaust amount of the internal combustion engine increases and therefore the NOx generation amount due to combustion increases, the NOx emission amount increases as the oxygen storage capacity of the exhaust purification catalyst decreases. Can effectively suppress the influence of the engine on the overall emission performance of the internal combustion engine. Therefore, in the present embodiment, the air-fuel ratio of the air-fuel mixture to be burned is slightly richer than the stoichiometric air-fuel ratio in the high load region of the internal combustion engine where the exhaust amount becomes large when the oxygen storage capacity of the exhaust purification catalyst decreases (for example, By setting “A / F = 14.4 to 14.5”), an increase in NOx emission accompanying a decrease in oxygen storage capacity is suppressed.

  Specifically, the electronic control unit 17 upwardly corrects the target output tVO of the oxygen sensor 24 in the sub-feedback control in the high load region of the internal combustion engine when the oxygen storage capacity of the exhaust purification catalyst is reduced to some extent. I am doing so. As described above, in the sub-feedback control, the output VAF of the air-fuel ratio sensor 23 is corrected with the sub F / B correction value VH set in accordance with the deviation between the output VO of the oxygen sensor 24 and the target output tVO. . Here, when the target output tVO is corrected upward, the voltage deviation ΔV is made smaller than the original, and the sub F / B correction value VH calculated by the above equation (6) is made larger than the original. become. Therefore, the value of the output VAFs of the air-fuel ratio sensor 23 after correction by the sub F / B correction value VH calculated in the above equation (5) is also made larger than the original value, and the actual air-fuel ratio ABF used in the main feedback control Becomes a value on the lean side of the actual air-fuel ratio. When the main F / B correction value DF is calculated using the actual air-fuel ratio ABF evaluated as an air-fuel ratio that is leaner than the actual air-fuel ratio in this way, even if the actual air-fuel ratio is the stoichiometric air-fuel ratio, from the control side. Thus, it is determined that the air-fuel ratio is still leaner than the stoichiometric air-fuel ratio. Therefore, when the target output tVO is corrected upward, air-fuel ratio feedback control is performed so that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio.

  As shown in FIG. 5, in the present embodiment, when the oxygen storage capacity of the exhaust purification catalyst is reduced, the engine operation region where the exhaust amount becomes large, here, the sub-air in the high load region where the intake air amount is equal to or greater than the specified value Y. The target air-fuel ratio in the feedback control, that is, the target output tVO of the oxygen sensor 24 is changed to a richer value than when the oxygen storage capacity is not lowered. As a result, an increase in NOx emission accompanying a decrease in oxygen storage capacity is effectively suppressed.

  However, when the target air-fuel ratio of the sub-feedback control in the high load range is changed in this way, in such a high load range, a value corresponding to the steady deviation of the actual air-fuel ratio with respect to the target air-fuel ratio changed to the rich side from the theoretical air-fuel ratio is set. As such, the sub F / B learning value SG is updated. Therefore, the value of the sub F / B learning value SG that should originally learn the steady deviation of the actual air-fuel ratio with respect to the stoichiometric air-fuel ratio becomes inappropriate. Therefore, in the present embodiment, as shown in the figure, the update of the sub F / B learning value SG is prohibited in the high load range of the internal combustion engine in which the target output tVO of the oxygen sensor 24 is corrected upward as described above. By setting the update prohibited area to be used, deterioration of the learning accuracy of the sub F / B learning value SG is avoided. That is, in the present embodiment, when the oxygen storage capacity of the exhaust purification catalyst is reduced, the learning area of the sub F / B learning value SG is limited to allow relatively free air-fuel ratio control that is not restricted by the learning. The engine operating area is secured. Such an engine operating region is set to a high load region in which the exhaust amount becomes large and the influence of the increase in the NOx emission amount on the overall emission performance becomes remarkable, and the target air-fuel ratio in the high load region is made rich. By changing to the side, the increase in the NOx emission amount accompanying the decrease in the oxygen storage capacity of the exhaust purification catalyst is effectively suppressed.

  FIG. 6 shows the oxygen storage capacity, NMHC (non-methane hydrocarbon) emission amount and NOx emission of the exhaust purification catalyst according to the travel distance of the vehicle in the in-vehicle internal combustion engine to which the fuel injection control device of this embodiment is applied. It shows the transition of quantity. Here, when the oxygen storage capacity of the exhaust purification catalyst is equal to or lower than the prescribed decrease judgment value shown in the figure, the change of the target air-fuel ratio to the rich side of the sub feedback control in the high load region as described above and the sub F / B Learning value SG is prohibited from being updated. As a result, the increase in the NOx emission amount due to the subsequent decrease in the oxygen storage capacity of the exhaust purification catalyst is suppressed, and a margin for the NOx emission amount for the regulation is sufficiently secured. On the other hand, depending on the change of the target air-fuel ratio to the rich side in the sub feedback control as described above, the NMHC emission amount increases as a contradiction. However, since the allowance for regulation is large for the NMHC emission amount, the allowance for regulation is still sufficiently maintained even if the emission amount increases.

  FIG. 7 shows the processing procedure of the sub-feedback routine employed in this embodiment. The processing of this routine is periodically executed by the electronic control unit 17 during engine operation as scheduled interruption processing.

  When the processing of this routine is started, the electronic control unit 17 first checks in step S10 whether or not the oxygen storage capacity of the exhaust purification catalyst has decreased below a specified decrease determination value. If the oxygen storage capacity is not lowered (S10: NO), the electronic control unit 17 performs normal sub-feedback control in step S20, that is, does not limit the learning region of the sub F / B learning value SG, and The sub-feedback control is performed by setting the target air-fuel ratio of the sub-feedback control in the engine operation region to the theoretical air-fuel ratio. On the other hand, when the oxygen storage capacity decreases (S10: YES), the electronic control unit 17 changes the target air-fuel ratio of the sub-feedback control in the high load region to a value slightly richer than the stoichiometric air-fuel ratio in step S30. In S40, updating of the sub F / B learning value SG in the high load range is prohibited, and sub feedback control is performed.

  In the fuel injection control device for the internal combustion engine of the present embodiment, the air-fuel ratio sensor 23 is the first oxygen sensor that detects the exhaust oxygen concentration on the exhaust upstream side of the exhaust purification catalyst, and the oxygen sensor 24 is the exhaust gas. The second oxygen sensor for detecting the exhaust oxygen concentration on the exhaust downstream side of the purification catalyst has a structure corresponding to each.

According to the fuel injection control device for an internal combustion engine of the present embodiment described above, the following effects can be obtained.
(1) In the present embodiment, when the oxygen storage capacity of the exhaust purification catalyst is lowered, the sub F / B learning value SG is prohibited from being updated in a high load region where the displacement is large. Further, when the oxygen storage capacity is reduced, the target output tVO of the oxygen sensor 24 corresponding to the target air-fuel ratio of the sub-feedback control in such a high load range is a value that makes the air-fuel ratio richer than when the oxygen storage capacity is not reduced. I am trying to change it. Since the engine operating region in which the target output tVO is changed is a large amount of NOx generated, the increase in NOx emission is a high load region in which the influence on the overall emission performance of the internal combustion engine is remarkable. While keeping the engine operating range for changing the fuel ratio to the minimum necessary, it is possible to effectively suppress the increase in the NOx emission amount accompanying the decrease in the oxygen storage capacity of the exhaust purification catalyst. In addition, in such a high load range, the update of the sub F / B learning value SG based on the sub F / B correction value VH is prohibited. Therefore, the target air-fuel ratio of the sub feedback control as described above is changed. The learning accuracy of the learning value SG is not affected. In addition, since the engine operation region where the update of the sub F / B learning value SG is prohibited is limited, the learning opportunity of the sub F / B learning value SG is also reduced to a necessary minimum. Therefore, according to the present embodiment, it is possible to suitably suppress an increase in the NOx emission amount when the oxygen storage capacity of the exhaust purification catalyst is lowered.

  (2) In the present embodiment, the air-fuel ratio sensor 23 for detecting the exhaust oxygen concentration on the exhaust upstream side of the exhaust purification catalyst and the oxygen sensor 24 for detecting the exhaust oxygen concentration on the exhaust upstream side of the exhaust purification catalyst are provided. I have to. Then, the main feedback control is performed by correcting the fuel injection amount in accordance with the deviation between the actual air-fuel ratio ABF calculated from the output VAF of the air-fuel ratio sensor 23 and the target air-fuel ratio, and the sub-feedback control is performed. This is done by correcting the output VAF of the air-fuel ratio sensor 23 according to the deviation between the output VO of the oxygen sensor 24 and the target output tVO of the sensor. When the air-fuel ratio feedback control is performed through the two feedbacks of the main feedback control and the sub-feedback control as described above, the change of the target air-fuel ratio of one of the two feedback controls is actually performed for the other feedback control. The air / fuel ratio of the engine may not be changed as desired. In this respect, in the present embodiment in which the main feedback control and the sub feedback control are performed in the above-described manner, the actual air-fuel ratio can be changed only by changing the target air-fuel ratio of the sub-feedback control set by the target output tVO of the oxygen sensor 24. Will be changed. Therefore, it is possible to appropriately suppress an increase in the NOx emission amount when the oxygen storage capacity of the exhaust purification catalyst is reduced without complicating the control structure.

In addition, the said embodiment can also be changed and implemented as follows.
In the above embodiment, when the oxygen storage capacity of the exhaust purification catalyst is reduced, the target output tVO of the oxygen sensor 24 corresponding to the target air-fuel ratio of the sub-feedback control in the high load region is changed, and in such a high load region The update of the sub F / B learning value SG is prohibited. However, even if the update of the sub F / B learning value SG is not completely prohibited, if the update degree of the sub F / B learning value SG in the high load region is lowered as compared with the other engine operation regions, the above is performed. A decrease in the learning accuracy of the sub F / B learning value SG due to a change in the target output tVO can be suppressed to some extent. Therefore, if the learning accuracy of the sub F / B learning value SG can be sufficiently secured, the updating of the sub F / B learning value SG in the high load range when the oxygen storage capacity is lowered is not completely prohibited. May be made lower than other engine operating regions. Note that the update degree of the sub F / B learning value SG is applied to the gradual change value when, for example, the ratio of the update amount SGK to the gradual change value of the sub F / B correction value VH is made smaller than usual or the update amount SGK is calculated. This can be done by making the width of the upper limit guard and the lower limit guard narrower than usual, or making the update frequency of the sub F / B learning value SG less than usual.

  In the above embodiment, the target fuel output tVO of the oxygen sensor 24 is changed so that the air-fuel ratio in the high load region when the oxygen storage capacity of the exhaust purification catalyst is reduced is made richer than the stoichiometric air-fuel ratio. This may be performed by changing the target air-fuel ratio in the main feedback control. If the target air-fuel ratio of the main feedback control is simply changed, the air-fuel ratio is returned to the stoichiometric air-fuel ratio by the sub-feedback control. Therefore, it is necessary to devise the control so as not to happen. Moreover, you may make it achieve the same objective by changing the control target of both main and sub feedback control.

The mode of main and sub feedback control in the above embodiment is not limited to the mode in the above embodiment, and may be changed as appropriate.
In the above embodiment, the air-fuel ratio feedback control is performed through the main and sub feedbacks. However, the present invention provides a fuel injection apparatus for an internal combustion engine that performs air-fuel ratio feedback control with only a single feedback. Can also be applied. In short, when the oxygen storage capacity of the exhaust purification catalyst decreases, the target air-fuel ratio of the air-fuel ratio feedback control in the engine operation region where the exhaust amount becomes large is changed to a richer side than when it is not decreased, and further such engine operation region If the update of the feedback learning value is prohibited or restricted in this way, it is possible to suitably suppress the increase in the NOx emission amount accompanying the decrease in the oxygen storage capacity.

  The present invention can be similarly applied to internal combustion engines other than the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows typically the whole structure about one Embodiment of the fuel-injection control apparatus of the internal combustion engine which concerns on this invention. The graph which shows the output characteristic of the air fuel ratio sensor employ | adopted as the embodiment. The graph which shows the output characteristic of the oxygen sensor employ | adopted as the same embodiment. The graph which shows transition of the oxygen storage capacity, NMHC discharge | emission amount, and NOx discharge | emission amount of the exhaust purification catalyst according to the vehicle travel distance when employ | adopting the conventional air fuel ratio feedback control. The graph which shows collectively the setting aspect of the target output of the oxygen sensor before and behind the oxygen storage capability fall in the said embodiment, and the setting aspect of the update prohibition area | region of the sub F / B learning value after oxygen storage capacity fall. The graph which shows transition of the oxygen storage capacity, the NMHC discharge | emission amount, and the NOx discharge | emission amount of the exhaust purification catalyst according to the vehicle travel distance in the same embodiment. The flowchart which shows the process sequence of the sub feedback routine applied to the embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Intake passage, 11 ... Throttle valve, 12 ... Combustion chamber, 13 ... Injector, 14 ... Exhaust passage, 15 ... Front catalytic converter, 16 ... Rear catalytic converter, 17 ... Electronic control unit, 18 ... Accelerator sensor, 19 ... Throttle Sensor: 20 ... Air flow meter, 21 ... NE sensor, 22 ... Fuel pressure sensor, 23 ... Air-fuel ratio sensor (first oxygen sensor), 24 ... Oxygen sensor (second oxygen sensor).

Claims (5)

Based on the detection result of the exhaust oxygen concentration, air-fuel ratio feedback control of the fuel injection amount is performed so that the air-fuel ratio of the air-fuel mixture combusted in the internal combustion engine becomes the target air-fuel ratio, and the fuel injection amount in the air-fuel ratio feedback control is controlled. In a fuel injection amount control device for an internal combustion engine that updates a feedback learning value based on a feedback correction value,
When the oxygen storage capacity of the exhaust purification catalyst is reduced, the target air-fuel ratio in the engine operation region where the exhaust amount becomes large is changed to a richer side than when the oxygen storage capacity is not reduced, and the target air-fuel ratio is made rich. A fuel injection control device for an internal combustion engine, wherein updating of the feedback learning value is prohibited in the engine operating region changed to the side. In the air-fuel ratio feedback control, a main feedback control based on the detection result of the exhaust oxygen concentration on the exhaust upstream side of the exhaust purification catalyst, and a sub feedback control based on the detection result of the exhaust oxygen concentration on the exhaust downstream side of the exhaust purification catalyst; As well as
The change of the target air-fuel ratio and the prohibition of update of the feedback learning value when the oxygen storage capacity of the exhaust purification catalyst is reduced are performed on the target air-fuel ratio and the feedback learning value for the sub-feedback control. The fuel injection control device for an internal combustion engine according to claim 1. Based on the detection result of the exhaust oxygen concentration, air-fuel ratio feedback control of the fuel injection amount is performed so that the air-fuel ratio of the air-fuel mixture combusted in the internal combustion engine becomes the target air-fuel ratio, and the fuel injection amount in the air-fuel ratio feedback control is controlled. In a fuel injection amount control device for an internal combustion engine that updates a feedback learning value based on a feedback correction value,
When the oxygen storage capacity of the exhaust purification catalyst is reduced, the target air-fuel ratio in the engine operation region where the exhaust amount becomes large is changed to a richer side than when the oxygen storage capacity is not reduced, and the target air-fuel ratio is made rich. A fuel injection control device for an internal combustion engine, wherein the degree of update of the feedback learning value in the engine operation region changed to the side is reduced as compared to other engine operation regions. In the air-fuel ratio feedback control, a main feedback control based on the detection result of the exhaust oxygen concentration on the exhaust upstream side of the exhaust purification catalyst, and a sub feedback control based on the detection result of the exhaust oxygen concentration on the exhaust downstream side of the exhaust purification catalyst; As well as
The change of the target air-fuel ratio and the reduction of the update degree of the feedback learning value when the oxygen storage capacity of the exhaust purification catalyst is reduced are performed on the target air-fuel ratio and feedback learning value of the sub-feedback control. The fuel injection control device for an internal combustion engine according to claim 3. A first oxygen sensor that detects an exhaust oxygen concentration upstream of the exhaust purification catalyst, and a second oxygen sensor that detects an exhaust oxygen concentration downstream of the exhaust purification catalyst;
The main feedback control is performed by correcting the fuel injection amount in accordance with a deviation between the actual air-fuel ratio calculated from the output of the first oxygen sensor and the target air-fuel ratio,
5. The internal combustion engine according to claim 2, wherein the sub feedback control is performed by correcting the output of the first oxygen sensor in accordance with a deviation between the output of the second oxygen sensor and a target output of the sensor. Fuel injection control device.

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